Bleaching fibrous material of natural cellulose



United States Patent 3,476,505 BLEACHING FIBROUS MATERIAL OF NATURAL CELLULOSE Uwe Kirner, Ludwigshafen (Rhine), and Bjarne Hartmark, Hambach, Weinstrasse, Germany, assignors to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany No Drawing. Filed Dec. 6, 1965, Ser. No. 511,988 Claims priority, application Germany, Dec. 10, 1964, B 79,687; May 7, 1965, B 81,807

Int. Cl. D061 3/16 U.S. Cl. 8139 6 Claims ABSTRACT OF THE DISCLOSURE Process of bleaching fibrous material of natural cellulose in the absence of oxidizing agents by treating the fibrous material with a liquid medium consisting essentially of an aqueous solution of certain amounts of (i) alkali metal hydroxide, (ii) alkali metal polyphosphates and/ or alkali metal salts of aminopolycarboxylic acids and (iii) anion-active and/or non-ionic wetting agents, the treatment being carried out under certain correlated temperature and time conditions between 90 C. and 150 C. and between 30 seconds and hours.

The present invention relates to a process for bleaching fibrous material of natural cellulose by treatment with alkali metal hydroxide solutions of definite concentration in the presence of sequestring agents.

It is a common practice to bleach fibrous material of natural cellulose, particularly of cotton, by treatment with very strong oxidizing agents, such as hydrogen peroxide, alkali metal hypochlorites and alkali metal chlorites. Although a satisfactory bleaching effect is achieved in this way, the cellulose undergoes appreciable damage by the oxidizing agent. Attempts to avoid the use of oxidizing agents and thus to prevent oxidative degradation of the cellulose during bleaching have hitherto been unsuccessful.

It is an object of the present invention to bleach fibrous material of natural cellulose without the use of oxidizing agents. Another object of the invention is to avoid fiber damage such as may be caused during bleaching by the oxygen of the atmosphere. It is a further object of the invention to bleach fibrous material of natural cellulose in a particularly simple and economical manner.

These objects are achieved in accordance with this invention by treating fibrous material of natural cellulose in the absence of oxidizing agents at a temperature of 90 to 150 C. for a period of from half a minute to five hours, preferably one minute to five hours, with an aqueous liquor which contains 4 to 13% by weight of alkali metal hydroxide together with 1 to 4% by weight of alkali metal polyphosphate and/or complex-forming alkali metal aminopolycarboxylilate, 0.5 to 3.0% by weight of anion-active and/or nonionic wetting agent which is active in alkaline solution, the treatment temperature t (measured in C.) within the specified range being so correlated to the treatment period 7 (measured in minutes) that it lies within the limits t and t (t denoting the lower limit, t denoting the upper limit, both limits inclusive) defined by the equations:

t =1 00-20* (log 7-1.5 (I) 11, :100-20 (log 1-4) (II) and freeing the material thus treated from alkali metal hydroxide, all percentages being with reference to the liquor. Instead of the alkali metal aminopolycarboxylate the free aminocarboxylic acid can be used inasmuch as 3,476,505 Patented Nov. 4, 1969 it is converted into the alkali metal salt in the alkaline liquor.

In principle the hydroxides of all the alkali metals may be used for the present process. Potassium hydroxide and sodium hydroxide are however preferred because of their easy accessibility and their very good efficacy.

Alkali metal polyphosphaes are defined as those which contain two or more phosphorus atoms in the molecule, combined together linearly or reticularly. Polyphosphates having the general formula: M P O (in which M denotes an alkali metal ion, preferably a sodium or potassium ion, and n denotes one of the integers from 2 to 10), for example sodium or potassium pyrophosphate, tripolyphosphate, tetrapolyphosphate and hexapolyphosphate and commercial mixtures of these polyphosphates are particularly emphasized. The polyphosphates of the said type may be used alone in the amounts stated above. These alkali metal polyphosphates are often referred to as alkali metal molecularly dehydrated polyphosphates.

Among the complex-forming aminopolycarboxylic acids, those having the general formula:

the integers 1 and 2, A denotes a radical having the formula -no-cn- H20 om Hie-0H2 or preferably m denotes zero, 1 or 2 and Y denotes identical or different groups having the formula -COOH or CH OH.

Examples of complex-forming aminopolycarboxlic acids are: N-hydroxyethylethylene diamine triacetic acid, o-cyclohexylene diamine tetracetic acid, diethylene triamine pentacetic acid, triethylene tetramine hexacetic acid, N-hydroxyethyldiethylene triamine tetracetic acid, nitrilotriacetic acid and particularly ethylene diamine tetracetic acid. The above-mentioned compounds may be used as alkali metal salts or as free acids, inasmuch as the acids are converted into the salts in the alkaline liquor.

The complex-forming aminopolycarboxylic acids or their alkali metal salts may be used alone instead of the polyphosphates in the amounts stated above. It has proved to be particularly suitable however to use the polyphosphates together with complex-forming aminopolycarboxylic acids or their alkali metal salts, the total concentration of the polyphosphates and aminopolycarboxylic acids or their salts in the treatment liquor being 1 to 4% by weight. Especially good bleaching results are achieved by using alkali metal polyphosphates and complex-forming aminopolycarboxylic acids or their salts in the weight ratio of 1:4 to 4:1.

The wetting agents may be conventional substances of this type which are active in alkaline solution. The manu facturers of wetting agents give information concerning the activity of their products in alkaline medium in their technical literature. They are generally products which are recommended as kier boiling assistants. Alkyl sulfonates, alkyl disulfonates, alkylaryl sulfonates, fatty acid condensates, protein cleavage products and sulfuric acid hemiesters of alkylphenol-ethylene oxide adducts or their salts are examples of anion-active wetting agents. Examples of nonionic Wetting agents are adducts of ethylene oxide to fatty alcohols, fatty acid amides, alkylnaphthols and alkylphenols. Mixtures of anion-active and nonionic wetting agents have proved to be particularly suitable. Examples of wetting agents which have proved to be very suitable are the following: sodium salt of the disulfonic acid of kogasin, diethanolamine salt of dodecylbenzene-sulfonic acid, sodium salt of bis-decanesulfonirnide, sodium salt of a sulfonated OC,fi-Olfifl having 12 to 14 carbon atoms, sodium salt of the sulfuric acid halfester of an adduct of 1 mole of nonyl phenol and 4 moles of ethylene oxide, adducts of 1 mole of colophony to 25 moles of ethylene oxide, of 1 mole of octyl phenol to 8 or 9 moles of ethylene oxide, of nonyl phenol to 10 moles of ethylene oxide, and of fatty alcohols of medium chain length, such as coconut fatty alcohol, to 7 to 9 moles of ethylene oxide, the condensation product of 2 moles of li-naphthalenesulfonic acid and 1 mole of formaldehyde, and particularly mixtures of several of these substances. The term kogasin denotes a hydrocarbon fraction from the Fischer-Tropsch sysnthesis having a boiling range of about 200 to 300 C. These mixtures are therefore preferred. The wetting agents may furthermore contain antifoaming agents, such as triisobutyl phosphate, in the usual way.

The liquor ratio, i.e. the ratio by weight of the textile material to the amount of liquor used, in the present process may be varied Within the range 0.5:1 to 3:1 and adapted to the apparatus available. It is preferable to use a liquor ratio of 0.8:1 to 2.521. This range is particularly suitable for continuous operation of the process. It is preferred to pad the treatment liquor onto the fibrous material and then to subject the impregnated material to the heat treatment. In general, the impregnated material is squeezed out in a padding machine to a liquor retention of 90 to 110% with reference to the weight of the dry fibrous material.

It is essential for the present process that the treatment temperature should be within the range of from 90 to 150 C. and should be correlated to the treatment period so that it does not fall short of or exceed the limits set by the abovementioned equations I and II. This means that for a given treatment period 1, the higher of the two lower limits 90 C. and t and the lower of the two higher limits 150 C. and t determine the temperature range to be used. When falling short of or exceeding the working range thus defined, the eifect of the treatment falls off so rapidly and so markedly that any appreciable whitening of the fibrous material no longer takes place.

Following the treatment, the fibrous material is freed from alkali metal hydroxide by conventional methods, for example by thorough rinsing and if necessary by acidification. Particularly good bleaching of the material being treated is obtained when it is rinsed at least once at boiling temperature to free it from alkali metal hydroxide. It has proved to be outstandingly suitable to carry out rinsing first twice at the boiling temperature and then once or twice at about 60 to 80 C., then to acidify with very dilute hydrochloric acid and finally to rinse once cold.

of the temperature range of 90 to 150 C. which may be used in the present process, the upper portion of the range from 110 to 150 (3., preferably from 115 to 150 C., is significant chiefly for short treatment periods up to about fifteen minutes, and the lower portion of the range from 90 to 110 0, preferably from 90 to 105 C., is significant chiefly for long treatment periods of from about thirty minutes. Particularly improved results are obtained when the concentration of alkali metal hydroxide within the range of concentration of from 4 to 13% is correlated to the treatment temperature in each of the said portions of the temperature range so that the concentration is low at the higher temperatures and high at the lower temperatures. A preferred embodiment of the process according to this invention therefore comprises choosing the concentration of alkali metal hydroxide in percent by weight so that in the upper portion of the temperature range from to 150 C., preferably from to 150 C., it remains within the limits c and c defined by the equations:

c =.100.1(t-100) (III) and c =12.50.1(t 100) (IV) and in the lower portion of the temperature range of 90 to 110 C., preferably 90 to 105 C., defined by the equations:

in dependence on the treatment temperature I in C.; the upper portion of the temperature range is preferably used for short treatment periods of up to fifteen minutes and the lower portion of the temperature range for long treatment periods of from thirty minutes.

The present process may be carried out batchwise or preferably continuously. In continuous operation the procedure may preferably be to carry out the treatment for thirty seconds to fifteen minutes, preferably from one to fifteen minutes, at temperatures of from to 150 C.

The process according to this invention permits the achievement, without oxidizing bleaching agents, of a bleaching effect which is better than that with a medium oxidizing bleach without damage to the fiber which occurs in oxidizing bleaching having to be tolerated. An even better degree of whiteness may be achieved by adding reducing bleaching agents, such as sodium dithionite, a-hydroxyalkanesulfinic acids and their salts, reaction products of a-hydroxyalkanesulfinic acids with ammonia or amines and salts of such reaction products, in amounts of at least 2.5% by Weight, to the bleaching liquor but for reasons of economy it is preferred not to use reducing agents in amounts which produce an appreciable additional bleaching effect. The addition of small amounts of reducing agent which are insufficient to effect bleaching, preferably of amounts up to 1.3% by weight, will however provide a very effective protection of the fibrous material from the destructive influence which atmospheric oxygen may exert under the working conditions. On the other hand, to achieve a strong additional bleaching effect it is very much more advantageous to carry out an additional reducing bleach following the present process. The abovementioned reducing bleaching agents may for example be used. The following working conditions have proved to be particularly suitable:

concentration of bleaching agent: 0.3 to 4% by Weight;

liquor ratio: 0.5 :1 to 50:1; duration of bleaching: one to sixty minutes at 90 to 150 C.

The invention is further illustrated by the following examples. The parts and percentages specified in the following examples are by weight. Prior to treatment according to this invention the cotton cloth mentioned in the examples had a degree of whiteness of 5 8 to 61%.

EXAMPLE 1 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

7.7% of sodium hydroxide,

2.0% of the tetrasodium salt of ethylenediamine tetracetic acid,

2.0% of a mixture of 35 parts of the diethanolamine salt of dodecylbenzenesulfonic acid and 18 parts of an adduct of 25 moles of ethylene oxide to 1 mole of colophony and 1.0 part of pine oil, and

0.3% of a mixture of 59 parts of sodium kogasin disulfonate and 8 parts of triisobutyl phosphate.

The material treated with the said solution is squeezed out on a padding machine to 100% liquor retention and treated with saturated steam at C. for ten minutes a cottage steamer. It is then rinsed with desalted water twice at 100 C. and one at 60 C. It is then acidified with an aqueous solution which contains 3 to 5 ml./l. of con centrated hydrochloric acid and again rinsed at room temperature.

A material entirely free from husks is obtained having a degree of whiteness which varies from 83.0 to 86.0% (measured on the Elrepho apparatus of the firm of Carl Zeiss, Oberkochen, with filter R 46 T) depending on the quality of the cotton.

EXAMPLE 2 Desized and dried unbleached coton cloth is impregnated with a solution having the following composition:

7.7% of sodium hydroxide,

2.0% of the trisodium salt of nitrilotriacetic acid, and as a wetting agent 2.0% of a mixture of 35 parts of the diethanolamine salt of dodecylbenzenesulfonic acid and 18 parts of an adduct of 25 moles of ethylene oxide to 1 mole of colophony and 1 part of pine oil, and

0.3% of a mixture of 59 parts of sodium kogasin sulfonate and 8 parts of triisobutyl phosphate.

The material treated with the said solution is squeezed out on a padding machine to 100% liquor retention and treated with saturated steam at 130 C. for fifteen minutes in a cottage steamer. It is then rinsed twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 m1./l. of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness, depending on the quality of the cotton, of 81.0% to 85.0% (measured as in Example 1).

The same result is obtained using an impregnating liquor which contains:

8.0% of sodium hydroxide,

2.0% of the tetrasodium salt of ethylenediamine tetracetic acid and one of the following wetting agents A to E:

(A) 1.8% of the sodium salt of the sulfuric acid hemiester of an adduct of 4 moles of ethylene oxide to 1 mole of nonyl phenol;

(B) 2.5% of a mixture of 5 parts of the adduct of moles of ethylene oxide to 1 mole of nonyl phenol, 57 parts of the sodium salt of the sulfuric acid hemister of an adduct of 4 moles of ethylene oxide to 1 mole of nonyl phenol and 10 parts of pine oil;

(C) 2.0% of a mixture of 10 parts of an adduct of 7 to 9 moles of ethylene oxide to 1 mole of fatty alcohol, 54 parts of the sodium salt of the sulfuric acid hemiester of an adduct of 4 moles of ethylene oxide to 1 mole of nonyl phenol and 5 parts of pine oil;

(D) 1.5% of a mixture of 10 parts of an adduct of 7 to 9 moles of ethylene oxide to 1 mole of fatty alcohol and 54 parts of the sodium salt of the sulfuric acid hemiester of an adduct of 4 moles of ethylene oxide to 1 mole of nonyl phenol and 0.3% of a mixture of 59 parts of sodium kogasin disulfonate and 8 parts of triisobutyl phosphate;

(E) 1.5 of a mixture of 5 parts of an adduct of 10 moles of ethylene oxide to 1 mole of nonyl phenol and 57 parts of the sodium salt of the sulfuric acid hemiester of an adduct of 4 moles of ethylene oxide to 1 mole of nonyl phenol and 0.3% of a mixture of 59 parts of sodium kogasin disulfonate and 8 parts of triisobutyl phosphate.

EXAMPLE 3 Desized and dried unbleached coton cloth is impregnated with a solution having the following composition:

7.7% of sodium hydroxide, 2.0% of the tetrasodium salt of ethylenediamine tetracetic acid,

2.0% of a mixture of 35 parts of the die'thanolamine salt of dodecylbenzenesulfonic acid, 18 parts of an adduct of 25 moles of ethylene oxide to 1 mole of colophony and 1 part of pine oil and 0.3% of a mixture of 59 parts of sodium kogasin disulfonate and 8 parts of triisobutyl phosphate.

The material which has been treated with the said solution is squeezed out to liquor retention on a padding machine and treated with saturated steam at 100 to 103 C. for three hours in a pad-roll plant. The plant should be equipped so that it can be operated free from air as far as possible. The material is then risend twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution which contains 3 to 5 ml./l. of concentrated hydrochloric acid and again rinsed at room temperature.

A completely husk-free material is obtained having a degree of whiteness, depending on the quality of the cotton, of from 82.0% to 85.0% (measured as in Example 1).

EXAMPLE 4 The procedure and conditions specified in Example 2 are adopted but using an impregnating liquor having the following composition:

8.0% of sodium hydroxide,

2.0% of the tetrasodium salt of ethylenediamine tetracetic acid,

2.0% of a mixture of 35 parts of the diethanolamine salt of dodecylbenzenesulfonic acid and 18 parts of an adduct of 25 moles of ethylene oxide to 1 mole of colophony and 1 part of pine oil,

0.3% of a mixture of 59 parts of sodium kogasin disulfonate and 8 parts of triisobutyl phosphate, and

1.5 of the sodium salt of imino-bis-methanesulfinic acid.

An entirely husk-free material is obtained having a degree of whiteness, depending on the quality of the material, of from 83.0% to 86.0%.

EXAMPLE 5 Desized and dried unbleached cotton cloth is impregnated with an aqueous solution having the following composition:

7.7 of sodium hydroxide,

2.0% of a mixture of 12 parts of an adduct of 8 to 9 moles of ethylene oxide to 1 mole of octyl phenol, 16.5 parts of the diethanolamine salt of dodecylbenzenesulfonic acid, 32 parts of sodium kogasin disulfonate, 5 parts of triisobutyl phosphate and 1.6 parts of a condensation product of 1 mole of formaldehyde and 2 moles of ,B-naphthalenesulfonic acid,

2.0% of one of the following substances or mixtures of substances:

(1) Sodium pyrophosphate;

(2) Sodium tripolyphosphate;

(3) Sodium hexametaphosphate;

(4) A mixture of 50 parts of sodium pyrophosphate and 50 parts of the tetrasodium salt of ethylenediamine tetracetic acid;

(5) A mixture of 50 parts of the trisodium salt of niltrilotriacetic acid and 50 parts of sodium hexametaphosp ate.

The impregnated material is squeezed out to 100% liquor retention on a padding machine and treated in a pad-roll plant with saturated steam for three hours at 100 to 103 C. The plant should be equipped to operate free from air as far as possible. The material is then rinsed twice at 100 C. and once at 60 C. with desalted water. It is then acidified with an aqueous solut1on containing 3 to 5 ml./l. of concentrated hydrochloric acid and rinsed again at room temperature.

A completely husk-free material is obtained having a degree of whiteness varying, depending on the quality 7 of the cotton, from 79.0% to 83.0% (measured as in Example 1).

EXAMPLE 6 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

6.5% of sodium hydroxide,

2.0% of a mixture of 12 parts of an adduct of 8 to 9 moles of ethylene oxide to 1 mole of octyl phenol, 16.5 parts of the diethanolamine salt of dodecylbenzenesulfonic acid, 32 parts of sodium kogasin disulfonate, parts of triisobutyl phosphate and 1.6 parts of a condensation product of 1 mole of formaldehyde and 2 moles of ,d-naphthalenesulfonic acid,

2.0% of one of the following substances or mixtures of substances:

(1) Sodium pyrophosphate;

(2) Sodium tripolyphosphate;

(3) Sodium hexametaphosphate;

(4) A mixture of 50 parts of sodiumhexarnetaphosphate and 50 parts of the tetrasodium salt of ethylenediamine tetracetic acid;

(5) A mixture of 25 parts of sodium tripolyphosphate and 75 parts of the tetrasodium salt of ethylenediamine tetracetic acid.

The impregnated material is squeezed out on a padding machine to 100% liquor retention and treated with saturated steam at 135 C. for ten minutes in a cottage steamer. Then it is rinsed twice at 100 C. and once at 60 C. with desalted water. It is then acidified with an aqueous solution containing 3 to 5 ml./l. of concentrated hydrochloric acid and again rinsed at room temperature.

A completely husk-free material is obtained which has a degree of whiteness, depending on the quality of the cotton, of from 80.0% to 84.0% (measured as in Example 1).

EXAMPLE 7 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

9.0% of potassium hydroxide,

3.0% of the tetrasodium salt of ethylenediamine tetraacetic acid,

1.0% of a mixture of 5 parts of sodium kogasin disulfonate, 2 parts of an adduct of 9 moles of ethylene oxide to 1 mole of octyl phenol, and 3 parts of the diethanolamine salt of dodecylbenzensulfonic acid.

The material treated with the said solution is squeezed out in a padding machine to 110% liquor retention and treated with a mixture of steam and air at 90 C. for 5 hours in a pad-roll plant. It is then rised twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 ml./l. of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness of 80.0% to 83.0% (meausl'ed as in Example 1).

EXAMPLE 8 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

4.5% of sodium hydroxide,

1.0% of the pentasodium salt of diethylentriamine pentacetic acid,

3.0% of sodium kogasin disulfonate.

The material'treated with the said solution is squeezed out in a padding machine to 90% liquor retention and treated with saturated steam at 110 C. for 4 hours in a cottage steamer. It is then rinsed twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 ml./l. of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness of 80.0% to 83.0% (measured as in Example 1).

EXAMPLE 9 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

10.0% of potassium hydroxide,

4.0% of sodium tetrapolyphosphate,

0.5% of a mixture of 5 parts of sodium kogasin disulfonate, 2 parts of an adduct of 9 moles of ethylene oxide to 1 mole of octyl phenol, and 3 parts of the diethanolamine salt of dodecylbenzenesulfonic acid.

The material treated with the said solution is squeezed out in a padding machine to liquor retention and treated with saturated steam at C. for 10 minutes in a cottage steamer. It is then rinsed twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 rnL/l. of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness of 78.0% to 82.0% (measured as in Example 1).

EXAMPLE 10 Desized and dried unbleached cotton cloth is treated in a jigger (which can be hermetically sealed) for two hours at a liquor ratio of 1:3 in a liquor having a temperature of C. and the following composition:

9.0% of potassium hydroxide,

1.0% of the tetrasodium salt of ethylenediamine tetraacetic acid,

0.5 of a mixture of 1 part of the sodium salt of bis-decanesulfonic acid imide, 2.5 parts of sodium kogasin disulfonate, and 1.5 parts of an adduct of 8 moles of ethylene oxide to 1 mole of octyl phenol.

It is then rinsed twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 ml./l of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness of 78.0% to 82.0% (measured as in Example 1).

EXAMPLE 11 Desized and dried unbleached cotton cloth is impregnated with a solution having the following composition:

6.0% of potassium hydroxide,

1.5% of the trisodium salt of nitrilotriacetic acid,

1.0% of the sodium salt of a sulfonated a,;3-olefin with 12 to 14 carbon atoms.

The material treated with the said solution is squeezed out in a padding machine to 100% liquor retention and treated with steam at C. for 1 minute in a cotton steamer. It is then rinsed twice at 100 C. and once at 60 C. with desalted water, then acidified with an aqueous solution containing 3 to 5 ml./l of concentrated hydrochloric acid and rinsed again at room temperature.

Material completely free from husks is obtained having a degree of whiteness of 80.0% to 84.0% (measured as in Example 1).

We claim:

1. A process for bleaching fibrous material of natural cellulose in the absence of oxidizing agents wherein the material is treated at a temperature within the range of 90 to 150 C. for a period of from thirty seconds to five hours with a liquid consisting essentially of an aqueous liquor containing the treatment temperature I (in C.) within the said range of 90 to 150 C. being so correlated to the period of treatment measured in minutes that it is within the limits t and t inclusive wherein I is the lower limit and t is the upper limit, and defined by the equations t =10020(log T 1.s (I) t =10020(log 7-4 (II) and freeing the material thus treated from alkali metal hydroxide.

2. A process according to claim 1 wherein the aqueous liquor contains (i) 4 to 13% by weight of an alkali metal hydroxide, (ii) 1 to 4% by weight of an alkali compopund selected from the class consisting of a polyphosphate of the formula M P O wherein M represent an alkali metal ion and n denotes one of the integers from 2 to and alkali metal salts of complex-forming aminopolycarboxylic acids of the general formula 110000112 our-00011 Y--CH ja CHzY wherein p represent one of the integers 1 or 2, A represents a radical selected from the group consisting of the formulae and wherein m denotes one of the integers 0, 1 and 2 and Y represents a member selected from the group consisting of carboxy and hydroxymethyl;

(iii) 0.5 to 3% by weight of a wetting agent selected from the group consisting of anion-active and nonionic wetting agents, which are active in alkaline solution.

3. A process according to claim 1 wherein the aqueous liquor contains (i) 4 to 13% by weight of an alkali metal hydroxide selected from the group consisting of sodium hydroxide and potassium hydroxide;

(ii) 1 to 4% by weight of a compound selected from the group consisting of alkali metal pyrophosphate, alkali metal tripolyphosphate, alkali metal tetrapolyphosphate, alkali metal hexapolyphosphate, alkali metal N-hydroxyethylethylene diamine triacetate, alkali metal ortho-cyclohexylene diamine tetracetate, alkali metal diethylene triamine pentacetate, alkali metal triethylene tetramine hexacetate, alkali metal N-hydroxyethyldiethylene triamine tetracetate, alkali metal nitrilo-triacetate and alkali metal ethylene diamine tetracetate and mixtures thereof;

(iii) 0.5% to 3% by weight of a wetting agent selected from the group consisting of anion-active and nonionic wetting agents, which are active in alkaline solution.

4. A process according to claim 1 wherein the liquor contains as component (ii) a mixture of (a) alkali metal polyphosphates and (b) complex-forming alkali amino polycarboxylates, the ratio of (a) to (b) by weight between 1:4 to 4:1.

5. A process according to claim 1 wherein the concentration c, measured in percent by weight, of the alkali metal hydroxide (i) is so correlated to the treatment temperature t in C. that it is between the limits c and 0 c representing the lower and c the upper concentration limits, both limits inclusive, as defined by the equations c 10-0.1 (t and 1 being a temperature in the range of from to C.

6. A process according to claim 1 wherein the concentration c, measured in percent by weight, of the alkali metal hydroxide (i) is correlated to the treatment temperature t in C. that it is between the limits c and c c representing the lower and 0 the upper concentration limits, both limits inclusive, as defined by the equations c =5.50.1(t-1O0) and c =8.5O.1(t100) I being a temperature in the range of from 90 to 110 C.

References Cited Kirner: Investigations to improve the alkaline pretreatment of Grey Cotton, Melli and Textilberichte, 9 1965, pp. 963-967.

MAYER WEINBLATT, Primary Examiner U.S. C1. X.R. s- 101 

